In space communications in the C, X, Ku, Ka, etc. band, with one or more satellites, some transmit/receive stations are equipped with antenna systems comprising a mount, said mount enabling the antenna to be pointed automatically at a traffic satellite, regardless of the position thereof in the sky. In other words, the mount enables adaptation of the transmitting and/or receiving direction of the antenna of the system. This adaptation is useful if, for example, an antenna on the ground must track the position of satellites in non-geostationary orbit. This feature is also useful if the antenna is onboard a mobile vehicle that must enable a communication link with a given satellite to be maintained. The equipment to which the antenna is fixed, i.e. the mount, must enable dynamic positioning thereof.
A plurality of types of mount exist in the prior art. For example, a mount of elevation over azimuth type may be used. The latter enables movement of the antenna about two axes, the first being the azimuth axis and the second the elevation axis. Its use is relatively inappropriate in the context of satellite telecommunication applications, notably when said satellites are at a high elevation. In fact, a singular point at the zenith is inherent to elevation over azimuth mounts. When the antenna is being elevated, i.e. when it is moving about the elevation axis, and reaches the zenith of its trajectory, the mount must effect a fast rotation of 180° about the azimuth axis for the antenna to continue its movement. The consequence of this rotation is rapid wear of the mount. Moreover, if said rotation is not fast enough, the current call may be interrupted.
A second family of mounts also exists. These are three-axis mounts. They have no singular point, but are bulky and relatively costly. Moreover, their high weight makes it difficult to envisage onboard use on small devices, notably on pilotless aircraft, also called “drones”.
It is also possible to use an electronically scanned antenna and dispense with the use of a mount, but this solution nevertheless encounters difficulties linked to its cost and its lack of precision.
A compromise suitable for satellite communications is obtained by the use of X-Y type mounts. These notably enable prevention of the occurrence of the singular point at the zenith and minimization of the weight and size of said mount. The singular point is not found at the zenith, as is the case for elevation over azimuth mounts, but horizontally, which is less problematic in the context of satellite applications, notably when the latter are positioned at high altitude (high-elevation satellites). This type of mount is compared to mounts of the elevation over azimuth type in the paper by A. J. Rolinski, D. J. Carlson and R. J. Croates entitled Satellite-tracking characteristics of the X-Y mount for data acquisition antennas, NASA technical note D-1697, Washington, D. C., June 1964.
In the remainder of the description, the movement of the antenna induced by the mount of the system of the invention may be described within a three-dimensional orthonormal frame of reference. The x and y axes are contained within the plane to which the base of the mount is fixed. By definition, the third axis z is perpendicular to that plane. If an X-Y mount is used, the movement of the antenna is the consequence of two rotation movements about two rotation axes/shafts X and Y, denoted by uppercase letters, unlike the axes x, y, z of the orthonormal frame of reference. The rotation axes X and Y are represented and their links with the various mechanical elements constituting the X-Y mount are highlighted in the remainder of the description.
Given the mechanical structure of X-Y mounts, balancing the various elements constituting them is then crucial and must be taken into account at the design stage and also to avoid having excessively high moments of inertia and serious and rapid wear, notably when the antenna in onboard an airframe. Thus it is important to balance the various elements of the antenna downlead included in the mount.